1. Field of the Invention
This invention relates in general to magnetoresistive (MR)heads for reading magnetically recorded data, and more particularly to a method and apparatus for providing a structure that achieves physical connection between the flux guide and the free layer and that insulates the flux guide from the shields.
2. Description of Related Art
Magnetic recording is a key and invaluable segment of the information-processing industry. While the basic principles are one hundred years old for early tape devices, and over forty years old for magnetic hard disk drives, an influx of technical innovations continues to extend the storage capacity and performance of magnetic recording products. For hard disk drives, the areal density or density of written data bits on the magnetic medium has increased by a factor of more than two million since the first disk drive was applied to data storage. Since 1991, areal density has grown by the well-known 60% compound growth rate, and this is based on corresponding improvements in heads, media, drive electronics, and mechanics.
Magnetic recording heads have been considered the most significant factor in areal-density growth. The ability of these components to both write and subsequently read magnetically recorded data from the medium at data densities well into the Gbits/in2 range gives hard disk drives the power to remain the dominant storage device for many years to come.
The heart of a computer is an assembly that is referred to as a magnetic disk drive. The disk drive includes a rotating magnetic disk, write and read heads that are suspended by a suspension arm above the rotating disk and an actuator that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The read and write heads are directly mounted on a slider that has an air-bearing surface (ABS). The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating. However, when the disk rotates, air is swirled by the rotating disk adjacent the ABS causing the slider to ride on an air bearing a slight distance from the surface of the rotating disk. The write and read heads are employed for writing magnetic impressions to and reading magnetic impressions from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
A magnetoresistive (MR) sensor detects magnetic field signals through the resistance changes of a sensing element, fabricated of a magnetic material, as a function of the strength and direction of magnetic flux being sensed by the sensing element. Conventional MR sensors, such as those used as a MR read heads for reading data in magnetic recording disk drives, operate on the basis of the anisotropic magnetoresistive (AMR) effect of the bulk magnetic material, which is typically permalloy (Ni81Fe19). A component of the read element resistance varies as the square of the cosine of the angle between the magnetization direction in the read element and the direction of sense current through the read element. Recorded data can be read from a magnetic medium, such as the disk in a disk drive, because the external magnetic field from the recorded magnetic medium (the signal field) causes a change in the direction of magnetization in the read element, which in turn causes a change in resistance of the read element and a corresponding change in the sensed current or voltage.
An MTJ device has been proposed as a magnetoresistive read head for magnetic recording in U.S. Pat. No. 5,390,061. A magnetic tunnel junction (MTJ) device is comprised of two ferromagnetic layers separated by a thin insulating tunnel barrier layer and is based on the phenomenon of spin-polarized electron tunneling. Such sensors are also referred to tunnel valve sensors. In such sensors, one of the ferromagnetic layers has a higher saturation field in one direction of an applied magnetic field, typically due to its higher coercivity than the other ferromagnetic layer. The insulating tunnel barrier layer is thin enough that quantum mechanical tunneling occurs between the ferromagnetic layers. The tunneling phenomenon is electron-spin dependent, making the magnetic response of the MTJ a function of the relative orientations and spin polarizations of the two ferromagnetic layers.
In an MTJ read head, the free ferromagnetic layer, the tunnel barrier layer and the fixed ferromagnetic layer all have their edges exposed at the sensing surface of the head, i.e., the air-bearing surface (ABS) of the air-bearing slider if the MTJ head is used in a magnetic recording disk drive. It has been discovered that when the MTJ head is lapped to form the ABS, it is possible that material from the free and fixed ferromagnetic layers will smear at the ABS and short out across the tunnel barrier layer. In addition, many antiferromagnets used to fix the magnetic moment of the fixed ferromagnetic layer contain manganese (Mn) which can corrode during the ABS lapping process. The tunnel barrier layer is typically formed of aluminum oxide, which can also corrode during the ABS lapping process. Accordingly, an tunnel valve read head for a magnetic recording system wherein the free ferromagnetic layer also acts as a flux guide to direct magnetic flux from the magnetic recording medium to the tunnel junction has been proposed to solve these problems. In a magnetic recording disk drive embodiment, the fixed ferromagnetic layer has its front edge recessed from the ABS while the sensing end of the free ferromagnetic layer is exposed at the ABS. The front edge of the tunnel barrier layer may also be recessed from the ABS. Both the fixed and free ferromagnetic layers are in contact with opposite surfaces of the tunnel barrier layer but the free ferromagnetic layer extends beyond the back edge of either the tunnel barrier layer or the fixed ferromagnetic layer, whichever back edge is closer to the sensing surface. This assures that the magnetic flux is non-zero in the tunnel junction region. The magnetization direction of the fixed ferromagnetic layer is fixed in a direction generally perpendicular to the ABS and thus to the disk surface, preferably by interfacial exchange coupling with an antiferromagnetic layer. The magnetization direction of the free ferromagnetic layer is aligned in a direction generally parallel to the surface of the ABS in the absence of an applied magnetic field and is free to rotate in the presence of applied magnetic fields from the magnetic recording disk. A layer of high coercivity hard magnetic material adjacent the sides of the free ferromagnetic layer longitudinally biases the magnetization of the free ferromagnetic layer in the preferred direction.
However, to prevent shunting of current, the flux guide needs to be insulated. To achieve high efficiency, it is necessary that there be no separation between the flux guide and the free layer.
It can be seen that there is a need for a method and apparatus for providing a structure that achieves physical connection between the flux guide and the free layer and that insulates the flux guide from the shields.